4fxyz electron orbital, computer model. An electron orbital is a region around an atomic nucleus (not seen) in which one or a pair of electrons is most likely to exist. The blue area is where an electron has a positive wavefunction, and the red area is where the wavefunction is negative. The 4fxyz orbital is part of the 4f shell, which contains seven orbitals in total. The 4f shell is partially full in the Lanthanide metals.